Hierarchical power systems are a standard feature for most aircraft and ground power distribution networks. An example of a typical hierarchical power system found in the prior art is illustrated in FIG. 1. Several levels of power distribution exist between a power source 1 and a variety of loads 3. Remote Power Controllers (RPCs) 5-16 are located at each level of the hierarchical power system. Each of the RPCs 5-16 isolates one or more of the loads 3, monitors current through a power switch (not shown) located within each of the RPCs 5-16, and responds by opening its power switch when a current limit or rating is reached. For example, if there is a fault at one of the loads 3, e.g., a short circuit to ground, any one of the RPCs 5-16 located on current path from the power source 1 to the faulted load may open its power switch, depending on which RPC 5-16 reaches its current limit or rating first. The RPCs at the upper hierarchical levels of a power system have higher current ratings and are generally located near the power source, while RPCs at the lower levels have lower current ratings and are generally located near loads. Current ratings for each of the RPCs 5-16 are given in FIG. 1.
The preferred packaging approach for RPCs is to place combinations of them in a single box, often called an Electrical Load Management Center (ELMC). There may be several of these ELMCs in a typical hierarchical power system. The prior art ELMC packaging approach gives rise to inherent inefficiencies and added system cost because the number of RPCs and their individual ratings are now fixed for a given ELMC design. A system designers' choices are now limited to the available ratings and quantities of RPCs which have been placed in a given ELMC. Further, the RPCs in the prior art ELMCs provide single, as opposed to parallel, current pathways from the source to the load. Standard ELMC designs are available, each having a certain selection of RPCs. For example, a Type 1 ELMC having eight 12 amp RPCs, a Type 2 ELMC having four 25 amp RPCs, a Type 3 ELMC having two 50 amp RPCs, a Type 4 ELMC having one 65 amp RPC, and a Type 5 ELMC having sixteen 3.5 amp RPCs and two 12 amp RPCs were established for the system of FIG. 1.
Specifically, FIG. 1 illustrates a hierarchical power system requiring a Type 4 ELMC, 17, tied at the first hierarchical level to the source 1, via input line 18. The output of ELMC 17 is connected at a second hierarchical level to a Type 3 ELMC, 19, and to a Type 2 ELMC, 21, via line 20. To accommodate the lower level of the power system, i.e. near the loads 3, the output of ELMC 19 is connected to a Type 2 ELMC, 23, and a Type 5 ELMC, 25, via line 24. Further the output of ELMC 21 is connected to a Type 5 ELMC, 27, and a Type 1 ELMC, 29, via line 28. Based on this example prior art system with the RPC ratings and quantities of the ELMC types given above, a total of 7 ELMCs of five different designs were required to complete the system. In addition, the system of FIG. 1 resulted in 43 unused RPCs (not shown) in the required ELMCs. The unused RPCs represent excess cost, weight, and design complexity in the system application.
Furthermore, the prior art ELMC design is not flexible enough to accommodate upgrades and enhancements that invariably occur in hierarchical power systems. System changes have to be made within the limitations of the unused RPCs available in the ELMCs found in the system. When system improvements require changes in load current ratings and/or location of power switches within the system hierarchy, the associated RPCs have to be replaced or additional RPCs added to meet the new system requirements.